The former secretary of state joined Lovato on stage and thanked her for speaking out on complex issues such as mental health.

"She is using her voice not only to sing and inspire us through that — she's using her voice to reach out to so many people who need a little bit of help themselves," Clinton said.

Lovato is just one of an army of surrogates blanketing Iowa this weekend, with only 10 days left until the caucuses.

A handful of college students told NBC News they were there to see Lovato — and were actually planning to support Bernie Sanders. But, for others, Clinton was the draw.

"Any time I see Hillary is going to be nearby, I make an effort to go," said one young woman. "But seeing Demi? That's just a bonus."

Clinton closed her short remarks by giving a nod to the singer-songwriter. She implored the crowd to join her "in helping to change our country, keep it on a progressive path, make sure we don't go back, we go forward, with confidence."

Hillary Clinton is joined by Demi Lovato at a campaign event in Iowa City, Iowa, on January 21, 2016.JIM YOUNG / Reuters